Most electronic devices emit electromagnetic radiation as a by-product of electrical and magnetic activity in the device during operation. These electromagnetic emissions from one device can interfere with the operation of other devices, causing potential problems. This interference in the electrical circuit of one device due to the electromagnetic radiations emitted by another device is termed electromagnetic interference (EMI). Any device containing electronic circuitry can produce EMI. Additionally, the presence of a radio transmitter within an electronic device dramatically increases emissions that can potentially cause interference, since the intentional emissions created by a radio transmitter are generally several orders of magnitude higher than the emissions produced by a non-transmitting device. EMI may interrupt, obstruct, or otherwise degrade or limit the effective performance of an affected electronic device. In some cases, the affected electronic device may be a device that performs a safety-related or other critical function, such as an electronic control system in an airplane.
The increasing use of personal wireless devices, such as cellular phones, in recent years has given rise to several safety concerns due to the risk of electromagnetic interference to electronic components of commercial aircraft. For example, modern commercial aircraft contain many electronic systems used in various communication, navigation, and system control functions. Some of these systems are wireless devices which intentionally transmit and receive electromagnetic signals at specific frequencies. If a cellular phone is operated within the airplane, the cellular phone may also transmit and receive electromagnetic signals. Depending upon the transmission characteristics of the cellular phone, the cellular phone may create EMI in one of the frequency bands used by aircraft systems, thereby compromising the normal operation of such systems. This concern has resulted in federal regulations prohibiting the operation of cellular phones and other personal electronic devices aboard airplanes and guidelines for evaluating aircraft systems to test their susceptibility to EMI.
Current employed methods for testing the susceptibility of electronic devices to EMI involve the use of a continuous wave (CW) signal generator to generate high levels of EMI within a specific frequency range. To test the susceptibility of a device to EMI generated by a cellular phone, EMI within the frequency range emitted by the phone will have to be created by the CW generator. However, the frequencies used by cellular phones are restricted and licensed by the FCC to local cellular network operators. The use of a CW signal generator at high power levels within these frequency bands is equivalent to the use of a cellular “jammer,” and is unlawful in the United States. Additionally, the EMI signals generated by a CW signal generator do not closely represent the type of EMI produced by a cellular phone. Cellular phones produce EMI characterized by short pulses at irregular intervals. A CW signal generator may not be able to accurately reproduce this type of EMI.
To truly characterize the susceptibility of an electronic device to cellular-phone-generated EMI, the device should be subjected to EMI of the type emitted by cellular phones, and the performance of the device evaluated. To ensure that a mission critical system will function properly in a worst-case scenario, the system should be tested while subjected to an unusually high level of EMI which retains the essential timing and waveform characteristics of the EMI produced by cellular phones. Embodiments of the invention described in this document include a system and a method for subjecting an electronic device to a particular form of EMI, namely, the type of EMI generated by cellular phones. This system is useful for the purpose of characterizing the susceptibility of electronic equipment to the specific levels and frequencies of EMI produced by modern cellular phones.
Although the systems described in this document have been configured to analyze the susceptibility of electronic devices to the type of EMI characteristic of cellular telephones, it is contemplated that embodiments of the invention may be broadly used to analyze the susceptibility of a device to any type of EMI. For example, systems based on the current disclosure may be used to evaluate the susceptibility of any type of industrial, defense, or medical equipment to interference from any EMI producing device.